1. Field of the Invention
This invention relates to a flying-spot type flaw detection system for detecting flaws existing in glass plate, plastic plate, or at least a plate material that transmits light (hereinafter referred to as a light-transmitting plate material) by scanning the light-transmitting plate material with a laser-light spot.
2. Description of the Prior Art
The flaw detection system for detecting flaws existing in a light-transmitting material is needed in a glass-plate manufacturing line, for example, to detect flaws present in glass plate being manufactured and feed back the detection results to the transparent glass plate manufacturing process, thereby preventing the recurrence of flaws at positions where they occur and improve product yield. Flaws in glass plate include bubbles formed by air bubbles remaining inside the glass plate, stones produced by foreign matter remaining in the glass plate, knots formed by almost molten foreign matter remaining inside the glass plate in a shape having streaming tail, cords which are knots having a very small width (0.1-0.2 mm), reams formed by the difference in refractive index caused by the difference in glass composition due to improper melting, etc.
Among flaw detection systems of conventional types included is a flying-spot type flaw detection system that scans glass plate with a light spot to detect with a light receptor changes in the optical axis of the transmitted light.
The flaw detection system of the conventional type has a high sensitivity only to changes in transmitted light in the direction of the manufacturing line. Since bubbles, knots and stones, which account for a great majority of flaws in glass plate, tend to cause significant changes in the light transmitted both in the direction of the manufacturing line and in the direction orthogonally intersecting the manufacturing line, they can be detected with the flying-spot flaw detection system of the conventional type. Flaws like cords and reams, however, cause no attenuation in the amount of transmitted light, resulting in very little changes in the light transmitted in the direction of the manufacturing line (about 1/100 as small as the changes in the case of bubbles). In addition, cords and reams, which are usually elongated in the direction of the line, cause changes only in the direction orthogonally intersecting the line. Thus, these flaws are hard to detect with the flying-spot flaw detection system of the conventional type.
It is an object of this invention to provide a flaw detection system that can detect not only flaws involving less optical changes, as represented by cords and reams, but also bubbles, knots, stones, etc.